This invention relates to a chemical copper-plating bath, particularly a chemical copper-plating bath capable of providing a plated film having excellent mechanical characteristics.
A chemical copper-plating bath generally contains a copper salt such as copper sulfate, cupric chloride, etc., a complex-forming agent such as ethylenediamine tetraacetate, N,N,N',N'-tetrakis-(2-hydroxypropyl)ethylenediamine, etc., a reducing agent such as formaldehyde and a pH controller such as sodium hydroxide, etc. Such a chemical copper-plating bath containing these components alone can give a plated film which is generally brittle and has only insufficient mechanical characteristics, especially poor ductility, for practical application. For example, according to the so called additive method, in which a current passage circuit portion is formed by chemical copper-plating on a printed circuit plate, circuit breaking is liable to occur due to processing of printed circuits, thermal strain caused by environmental changes or physical impact.
In order to improve the above drawbacks, there have been attempts to improve ductility of a chemically deposited copper film by adding polyethylene glycol, dipyridyls, phenanthrolines or water-soluble cyanides to a chemical copper-plating bath comprising a copper salt, a complex-forming agent, a reducing agent and a pH controller. However, even if the above dipyridyls may be added, improvement in ductility of the chemically deposited copper film is very slight, and the mechanical characteristics attained are still insufficient for practical application, for example, as a copper film for forming the current passage circuit in printed circuits.